Magnetron discharge tube for frequency multiplication



July 18, 1939. K. FRITZ 2,166,210

MAGNETRON DISCHARGE TUBE FOR FREQUENCY MULTIPLICATION Filed Nov. 16,1937 y XI/S2 MAGNET/6 1 man ma F/ELD ENVELOPE: Maox 512 510 cuppa/rTHROUGH GAPS BETWEEN INNER ANODES our/ w wean/r caupoA/mr/l 01/5 70MUU/PZE FREQUENCY rum/6 0F OUTPUT RESUUZ/VT aurpur CURRENT III/E196MAG/V67 SAMEAS F/G. .3 BUT /NPU T AND OUTPUT CIRCUITS TUNED T0 SAMEFREQUENCY lMPl/LSE (INA/para emu/r OUTPUT CURRENT COMRUNENT DUE T 0TRIPLE FREQUENCY T UN/NG RESUL TANT OUTPUT CURRENT INVENTOR KARL FRITZBY v ATTORNEY Patented July 18, 1939 UNITED STATES PATENT OFFICEMAGNETRON DISCHARGE TUBE FOR FREQUENCY MULTIPLICATION GermanyApplication November 16, 1937, Serial No. 174,772 In Germany October 30,1936 6 Claims.

This invention relates to magnetron discharge tubes and circuitarrangements therefor. More particularly, it concerns a frequencymultiplier including a magnetron discharge tube in which pairs ofalternating current-carrying anodes are disposed at different distancesfrom the cathode.

It has been suggested in the prior art that segmented anode magnetronsmay be employed for frequency multiplication. It was usual in such casesto have two control segments and two power segments. I shall presentlygive a brief description of the prior art system in order to betterexplain my improvements thereover.

The accompanying drawing includes five figures, of which Figure 1 is adiagram of a magnetron discharge tube designed substantially inaccordance with conventional practice,

Fig. 2 is a corresponding diagram intended to show the improvements ofthis invention, and

Figs. 3, 4 and 5 are representations of wave formations obtainable underdifferent conditions of operation of a magnetron discharge tube.

Referring first to Fig. l, I show therein a magnetron discharge tube Rhaving a cathode K, a pair of inner anodes J1 and J2, and a pair ofouter anodes A1 and A2. The anodes of each pair are symmetricallydisposed about the oathode. The outer electrodes A1 and A2 areelectrically interconnected directly through a loop B. Between the twoinner or control electrodes J1 and. J2 is the control circuit St whichnormally is fed with an alternating potential having a frequency w froman outside source of control or master potential.

The outer or energy electrodes A1 and A2, with the interposition of anoscillatory circuit tuned to control frequency, would operate inpush-pull. Upon each alternation or half-cycle of the controloscillation a rush or pulse of current arises in the joint plate oranode lead of the two electrodes A1 and A2. These current pulses,inasmuch as they are of a frequency twice that of the controloscillations,

5 may excite an oscillation circuit 0 inserted between the loop B andthe cathode K, and the said oscillatory circuit must then be tuned to aWave twice the control frequency.

The arrangement just described has the short- 50 coming that the controlof the oscillations generated is not symmetric because the outputcircuit is uni-laterally grounded through the comparatively highcapacitances of the source of potential. Moreover, difliculties arise onaccount 55 of the relatively long connecting leads.

My improved magnetron circuit organization is adapted for frequencymultiplication by the aid of a specially designed magnetron in which thealternating current carrying electrodes are mounted at differentdistances from the cathode 5 and comprise an even number of segments. Italso has this outstanding characteristic feature that the controlelectrodes adjacent the cathode are fed through an oscillation circuittuned to the fundamental frequency of the control potenl0 tial, and thatan output circuit is connected between the power segments which arelocated outwardly from the control segments. The oscillations after theyhave been multiplied in frequency are also preferably amplified.Moreover, the de- 15 gree of saturation of the magnetic field and/or thebiasing direct current voltages of the various segments are so chosen asto advantageously determine the shape of the generated wave. The currentwave shape in the output circuit may 20 also differ from that of thecontrol current.

If the frequency multiplication is to be at an odd ratio, say, at theratio of 1:3, then the various segments of the electrode systems areimpressed with like biasing potentials. The mag- 25 netic field is thenmade so powerful that electrons will emerge from the control system onlyduring the negative and the positive crest values of the controlpotential, while the length of flow of current to the power electrodesis less than /2 30 or more particularly equal to or less than of thetime T of a control oscillation. The current curves in this scheme needby no means be of rectangular shape, though they should substantiallydiffer, say, from the sine shape of the con- 35 trol potential.

If frequency multiplication is to be at an even ratio, more particularlyfrequency doubling, then the intensity of the magnetic field is maderoughly normal, while the various segments of one or 40 of both systems,or more particularly only the segments of the power system, areimpressed with positive biasing voltage of different values as comparedwith the cathode. The difierence between these biasing voltages and alsothe absolute value of the biasing voltages must be so chosen that theelectrons, during both alternations of the control oscillations, willflow over predominantly to the same segment.or to one and the same groupof segments. Of course, this means that no uninterrupted direct currentmust arise, but that the size of the current which flows over to theimpacted segment varies between a minimum and a finite maximum value.

The actions inside the tube and above all the current intake or currentpassages to the various segments of the power system are shown in moredetail in Figs. 3 to 5 inclusive. It should be noted that the outputcircuit, similarly as in sim ple amplifier arrangements, is interposedbetween the segments or segment groups of the power systems, and thatradio frequency current is kept away from the cathode.

Fig. 2 shows a practical embodiment of the idea underlying the inventionas incorporated in a twin-system master-control tube. The followingdescription is not intended, however, to restrict the invention to thisform of construction. The constant electric and magnetic fields are sochosen that electrons will fly through the slits or gaps between theelectrodes J1 and J; of the inner system, provided, however, that anelectric cross field prevails between these inner electrodes, the latterbeing intended to exercise a control action. In such a case, as will beremembered, alternate control of the current is possible. These currentflows, which for the time being may be assumed to be of sinuous form,will contribute to a reduction of damping in the outer power system onlywhen they pass at the proper phase through the oscillatory cross-fieldwhich is set up between the outer segments A1 and A2. But, if the outputcircuit is tuned to a different frequency, then the fiow of currentthrough the gap or split-plane of the inner system (which plays the mostessential part) is determined by the superposition of the twoalternating potentials which arise in the inner and the outer systems.

As shown both in Fig. 1 and Fig. 2 the leads to the outer electrodes A1and A2 are constituted by a twin conductor system B having distributedinductance and capacitance. Another twin conductor system havingdistributed inductance and capacitance forms part of the input circuitconnected to the inner anode segments J1 and 52. The last mentioned twinconductor system a is preferably arranged at right angles to the firstmentioned twin conductor system.

Referring to Fig. 3, the dash line illustrates the flow of currentthrough the split-plane of the control system St, if only the controlalternating voltage is present. The output circuit O, for instance, forthe object of doubling, is tuned to a frequency twice as high, andincidentally, as is usual, the system starts oscillating spontaneously.Under the influence of the alternating potentials of the outer systemalone the wave shape of current flow should be represented in accordancewith the known current distribution principle ap plying to multi-splitanode magnetrons. Such a wave shape is as indicated by the dotted line.Upon the superposition of both alternating potentials there results thesolid heavy line which reflects actual flow of current to the outersystern. The phase between the two control potentials is so chosen as toobtain maximum efficiency. It is found that a distinct generation of thedouble frequency occurs side by side with an appreciable residue of thefundamental frequency. An essential improvement of this action issecured by suppressing the fundamental, for instance, by inverting analternation. Fig. 2 shows that by raised or reduced biasing voltage uponone of the two outer segments A the flow of current which is controlledfrom the fundamental wave is practically or predominantly only in oneand the same direction through the splitplane of the control system. Theheavy solid line in Fig. 4 again illustrates the superposition of theother two graphs. In other words, as contrasted with Fig. 3, there is anincrease in amplitude of the doubled frequency, while the controlfrequency or fundamental frequency practically disappears. A similarsituation results also for multiplicationsof a higher order.

In case of odd multiplications, however, with a view to insuring highefficiency it is best to employ a non-sinuous and preferably an impulsewave in the control system. Referring to Fig. 5, the dotted linerepresents the control alternating potential for the inner system. Byraising the intensity of the magnetic field, conditions may be made sothat the emergence or outflow of current will occur only in the presenceof a certain amplitude of the alternating potential. Accordingly, thereresult current pulses as indicated by the dash line. By superpositionwith the control effect or control potential (dotted line) of theexcited output circuit, which, for instance, has been tuned to thetriple frequency, there results an actual potential at the outer systemsuch as shown by the dot-dash line. Upon energy absorption this waveseems to be slightly damped and then excited again. A similar situationholds good for the higher multiplications.

Experiments along these lines have shown that in odd-frequencygeneration there is a failure to maintain fixed phase relations betweenthe control energy and the output energy. That is to say, the phase isconstantly subject to change. And this exactly agrees with mathematicalfindings.

It was further ascertained by practical experiments with multiplicationsof a high order that a critical adjustment of the magnetic field wasrequired as well as sharp tuning to the desired short wave. Otherwisethe operation of the multiplier would become uncertain. There is eithera tendency for the fundamental wave to become excited in the outputcircuit, or else several harmonic waves of a higher order are generated.

When comparatively large currents are dealt with, especially whenworking with brief current pulses only, the electrons will be held backbetween the segments of the control system for relatively long periodsof time. The result is that an unduly large space charge is built up inthe vicinity of the cathode. Among the electrons thus retained a greatmany return again to the cathode and cause additional heating of thesame. In order to remedy this shortcoming and difficulty it ispreferable to mount an apertured auxiliary electrode G in closeproximity to the oathode. This auxiliary electrode may be a grid incoiled form upon which is impressed cathode po tential or a slightlypositive potential. The Faraday cage-11k structure about the cathodecollects the alternating components from the cathode so that additionalheating avoided.

It has been found expedient to place the electrodes of the controlsystem in an inclined posi ticn in reference to the cathode in such away that theelectrodes which roughly have the form of segments of aprismatic hollow body or hollow cylinder present a slope similar to thelateral surfaces of a pyramid or a cone in reference to thecorresponding axis. The result is that the electric field contains aslightly axial component in addition to the radial component. Theelectrons during their looped trajectories or paths of flow, moveadditionally to a slight degree in the direction of the axis ofsymmetry, that is, towards the base of an imagined pyramid. By thisartifice the exit of the electrons from the control system is promoted.A similar effect is obtainable also by providing some other dissymmetryeither electrical or magnetic of the field pattern.

The circuit organization could also be used directly for the productionof oscillations, say, in such a way that the inner system is operated ina self-oscillatory scheme. But in most instances the control or insidesystem will be fed with oscillations Whose frequency is stabilized,especially when the frequency multiplier tube is to furnish theheterodyne oscillations for a high-quality receiver. For a multi-stagemaster-excited transmitter, of course, the same basic rules will apply.

What precedes does not apply, of course, merely to the actions observedin multi-split magnetrons, but holds good whenever the current isinfluenced both by the fundamental controlling system as well as by theoutput system.

I claim:

1. A circuit organization adapted for frequency multiplication having amagnetron discharge tube containing a cathode and a plurality ofsegmented anodes mounted at unequal distances from the cathode, theouter anode segments be ing equal to the inner segments in number, meansincluding a direct current source for impressing suitable biaspotentials on said electrodes, means for impressing control potentialsupon the electrode system adjacent the cathode, an oscillation circuitconnected to the control electrode system and tuned to the fundamentalfrequency, means for projecting periodic clouds of electrons between theinner segments and toward the outer electrode assembly, means includingan output circuit connected between the outer electrodes and the cathodefor deriving oscillations of multiplied frequency, and means foradjusting the strength of the magnetic field and the value of the directcurrent biasing potentials on the various segments to suitable valuesfor obtaining frequency multiplication at optimum efficiency.

2. A circuit organization adapted for frequency multiplication asclaimed in claim 1, with the characteristic feature that the varioussegments of the electrode systems are impressed with biasing potentialsthat are alike in reference to one another, and that the magnetic fieldis chosen so powerful that from the control system electrons are causedto emerge only during the negative and positive crest values of thecontrol potential, and that the duration or length of current passage orelectron flow to the outer anode segments is less than 12, andpreferably equal to or less than one-sixth of the duration of a controlos cillation, whereby an odd harmonic of the funda mental frequency isobtained.

3. A circuit organization adapted for frequency multiplication asclaimed in claim 1 with the characteristic feature that the variouspairs of segments are impressed with different positive biasingpotentials in reefrence to the cathode, the said biasing potentialsbeing of such values that the electrons, during both halves of a cycleof a control oscillation flow predominantly towards the same segment,whereby an even harmonic of the fundamental frequency is obtained.

4. A circuit organization as claimed in claim 1 and comprising atwin-conductor system with distributed inductance and capacity formingpart of the output circuit, and having an additional twin-conductorsystem constituted by a reactive impedance to the multiplied wavedisposed in the input circuit and perpendicular to the twin-conductorline of the output circuit, said reactance being adapted to stabilizethe frequency of the fundamental wave.

5. A circuit organization as claimed in claim 1 and having a gridelectrode disposed in close proximity to the cathode, and means formaintaining said grid electrode substantially at cathode potential.

6. A high frequency generating system comprising a magnetron dischargetube having a centrally disposed linear cathode and a plurality ofcylindrioally segmented anodes, said anodes being constituted by twosystems one within another, and the axis of at least one of said systemsbeing at a slight angle to the axis of said cathode.

KARL FRITZ.

